The long-term goals of this application are to study the functional roles of gap junctional intercellular communication in vascular and retinal biology. There are three specific aims. 1) The connexin37/connexin40 (Cx37-/-/Cx40 -/-) double knockout mouse shows evidence of vascular leakage of both red cells and fluid at selected locations. The sites of leakage will be precisely mapped by studies using vascular permeability tracers. Primary endothelial cell cultures will be used to study regulatory mechanisms involved in this process. In addition, temporally controlled, site-specific deletion of Cx37 will be mediated by a tamoxifen- inducible chimeric Cre recombinase driven by the endothelium-specific Tie-2 promoter. When these animals are mated with viable, fertile Cx40 -/- animals, Cx37-/-/Cx40 -/- conditional mutants will result, permitting a detailed study of the vascular defects in mice. 2) Cx36 is a neuron-specific member of the gap junction connexin gene family. A Cx36-"- animal has been developed by insertion of a bicistronic reporter expressing 13-galactosidase and human alkaline phosphatase, permitting characterization of the retinal neurons expressing Cx36. Changes in gap junctional communication in the retina as a result of the loss of Cx36 will be studied. 3) A systematic study of the retina has revealed that two other connexins, Cx45 and Cx57 are also expressed by retinal neurons. Using immunohistochemistry and in situ hybridization, the cellular locations of these connexins will be precisely determined. If these connexins are expressed in retinal neurons, mouse lines with targeted gene knockouts of these connexins will be prepared and studied for functional consequences.